DE69613961T2 - METHOD FOR THE PRODUCTION OF RUTHENIUM COMPLEXES AND THEIR USE AS IN SITU HYDROGENATING CATALYSTS - Google Patents

Description

FIELD OF INVENTION

This invention provides a process for preparing ruthenium complexes. These complexes can be prepared and used in situ as catalysts in the hydrogenation of unsaturated substrates and are particularly useful in the hydrogenation of nitriles.

TECHNICAL BACKGROUND

J. P. Genet, S. Mallart, C. Pinel, S. Juge and J. A. Laffitte, Tet. Assym., 1991, vol. 2, p. 43, report on the reaction of (COD)Ru(2-methallyl)2 with chiral bidentate phosphines to give Ru(P-P)(2-methylallyl)2 complexes which, under hydrogen, catalyzed the hydrogenation of olefins. The ruthenium complexes prepared under hydrogen were not isolated or characterized.

B. Chaudret and R. Poilblanc, Organometallics, 1985, vol. 4, p. 1722, describe the hydrogenation of the Ru(0)-olefin complex Ru(COD)(COT) in the presence of tricyclohexylphosphine to give RuH₂(H₂)₂(PCy₃)₂.

J. Powell and B. L. Shaw, J. Chem. Soc. (A); 1968, p. 159, describe the preparation of allyl complexes of ruthenium(II), Ru(all)2(diolefin), where all = allyl or 2-methylallyl and diolefin = norbornadiene or 1,5-cyclooctadiene.

M. Cooke, R. J. Goodfellow, M. Green and G. Parker, J. Chem. Soc. (A), 1971, p. 16, describe the reaction of cyclooctadieneruthenium bis(methylallyl) with phosphorus ligands to give (P-ligand)2Ru(2-methylallyl)2.

W. H. Knoth, U.S. Patent 3,538,133, describes the preparation of RuH2(Q2)(PPh3)3, where Q is H or N, and several other closely related ruthenium complexes by reaction of RuHCl(PPh3)3 with triethylaluminum or sodium borohydride. However, the procedures used to prepare the required RuHCl(PPh3)3 starting material are only applicable to closely related triarylphosphines, therefore the chemistry described by Knoth is not broadly applicable to a wide range of PR3 ligands.

SUMMARY OF THE INVENTION

This invention provides a process for the in situ preparation of a ruthenium complex of Formula I, RuH₂(PR₃)₂L₂, wherein:

each PR3 is an organophosphorus ligand, present as a separate ligand or linked to at least one other organophosphorus ligand;

each R is a substituent independently selected from: H, R', OR', OSiR'₃, NH₂, NHR' and NR'₂;

each R' is independently selected from: a hydrocarbyl group and an array of at least two hydrocarbyl groups linked by ether or amine linkages;

each L is a ligand selected from: H2 and an additional equivalent of the organophosphorus ligand PR3;;

comprising contacting a ruthenium compound having the formula R²₂RuA₂, wherein R² is a mono- or poly-, cyclic or acyclic alkene ligand present as either two separate ligands or as a single polyalkene ligand, and A is an allyl ligand or a hydrocarbyl substituted allyl ligand, an organic solvent and PR₃, wherein the molar ratio of PR₃ to the ruthenium compounds is at least 2:1, with gaseous hydrogen; stirring the solution at a temperature of about -30°C to about 200°C; and optionally isolating the ruthenium complex from the organic solvent.

DETAILED DESCRIPTION OF THE INVENTION

The ruthenium complexes of formula I are useful as catalysts in the rapid hydrogenation of substrates such as alkenes, which are typically easy to hydrogenate. However, their main value lies in their ability to hydrogenate nitrile groups, which are generally considered very difficult to hydrogenate. With dinitriles, the catalysts allow the preparation of the aminonitriles as intermediates with high selectivity.

The starting material for processes of the present invention for preparing ruthenium complexes of formula I comprises ruthenium compounds having the formula R22RuA2, where R2 represents an alkene ligand and A represents an allyl ligand or hydrocarbyl-substituted allyl ligand. The alkene ligands are straight chain, branched or cyclic arrangements of carbon atoms connected by single, double or triple carbon-carbon bonds comprising at least one carbon-carbon double bond and substituted with hydrogen atoms as appropriate. The alkene ligands may be present either as two separate ligands or as a single polyalkene ligand. Polyalkene ligands such as cycloheptatriene, norbornadiene and 1,5-cyclooctadiene (COD) are preferred, with 1,5-cyclooctadiene being most preferred.

The ruthenium compound R22RuA2 can be prepared by reacting R22RuX2, where the alkene ligand is as described above and X is halide or pseudohalogen (e.g. the anion of a salt of a protonic acid such as nitrate or acetate), with a suitable Grignard reagent, for example 2-methylallylmagnesium chloride or allylmagnesium chloride, as described in Powell and Shaw, J. Chem. Soc. (A), 1968, 159. Such Grignard reagents are usually prepared by reacting the corresponding allyl halide with magnesium metal. Since a very large number of allyl halides are known and possible, a very wide variety of A ligands can be considered, but since simple, inexpensive A ligands work just as well as more complex ligands, the choice of A ligand is ultimately determined by cost and availability. Examples of preferred A ligands include allyl, 1-methylallyl, and 2-methylallyl, with 2-methylallyl being the most preferred.

In formula I, PR₃ represents an organophosphorus ligand wherein each R is a substituent independently selected from the group consisting of H, R', OR', OSiR'₃, NH₂, NHR' and NR'₂, wherein each R' is a hydrocarbyl group or an arrangement of at least two hydrocarbyl groups linked by ether or amine bonds. Organophosphorus ligands include phosphines, phosphinites, phosphonites and phosphites. Hydrocarbyl group means a straight chain, branched or cyclic arrangement of carbon atoms linked by single, double or triple carbon-carbon bonds and substituted accordingly with hydrogen atoms. Such Hydrocarbyl groups can be aromatic and/or aliphatic, for example phenyl, aryl, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl and aralkyl. Arrangements of at least two hydrocarbyl groups linked by ether or amine bonds include alkoxy, aryloxy, pyridyl and aminoalkyl groups. Suitable hydrocarbyl groups or arrangements of hydrocarbyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, benzyl, phenyl, naphthyl, o-tolyl, m-tolyl, p-tolyl, xylyl, vinyl, allyl, butenyl, cyclohexene yl and cyclooctenyl, β-methoxyethyl, 4-methoxybutyl, 2-pyridyl, 4-(N,N-dimethylamino)butyl and 2-methoxyphenyl.

Typical examples of organophosphorus PR3 ligands include cyclohexylphosphine, phenylphosphine, diethylphosphine, dicyclohexylphosphine, diphenylphosphine, trimethylphosphine, triethylphosphine, tri-n-propylphosphine, triisopropylphosphine, tri-n-butylphosphine, triisobutylphosphine, tri-t-butylphosphine, triphenylphosphine, tricyclohexylphosphine sphinx, Tribenzylphosphine, tris(2-pyridyl)phosphine, tri-p-tolylphosphine, tris(p-trifluoromethylphenyl)phosphine, o-diphenylphosphino-N,Ndimethylaniline, (3-N,N-dimethylaminopropyl)diisopropylphosphine, (4-N,N- Dimethylaminobutyl)-diisopropylphosphine, diphenylmethylphosphine, dimethylphenylphosphine, dicyclohexyl(β-methoxyethyl)phosphine and bis(β-methoxyethyl)phenylphosphine.

Other typical examples of PR3 ligands include cyclohexyl phosphite, phenyl phosphite, diethyl phosphite, dicyclohexyl phosphite, diphenyl phosphite, trimethyl phosphite, triethyl phosphite, tri-npropyl phosphite, triisopropyl phosphite, tri-n-butyl phosphite, triisobutyl phosphite, tri-t-butyl phosphite, triphenyl phosphite , tricyclohexyl phosphite, tribenzyl phosphite, Tris (2-pyridyl)phosphite, tri-p-tolylphosphite, tris(p-trifluoromethylphenyl)phosphite, tris(trimethylsilyl)phosphite, methyldiphenylphosphinite, ethyldiphenylphosphinite, isopropyldiphenylphosphinite, phenyldiphenylphosphinite, diphenylphenylphosphonite, Dimethylphenylphosphonite, diethylmethylphosphonite and diisopropylphenylphosphonite.

Two or more PR₃ organophosphorus ligands can be linked together to form diphosphorus, triphosphorus or polyphosphorus ligands. Examples of such diphosphine ligands include 1,2-bis(dimethylphosphino)ethane, 1,2-bis(diethylphosphino)ethane, 1,2- bis(dicyclohexylphosphino)ethane, bis(dicyclohexylphosphino)methane, 1,2-bis[(β-methoxyethyl)phosphino]ethane, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,2-bis(diphenylphosphino)benzene, (-)-1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene, (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, bis(2-diphenylphosphinoethyl)phenylphosphine, tris(2-diphenylphosphinoethyl)phosphine and 1,1,1-tris(diphenylphosphinomethyl)ethane.

Diphosphites, diphosphinites such as bis(diphenylphosphinito)-2,2'-1,1-binaphthyl, and diphosphonites can also be used as PR3 ligand.

PR3 ligands can also be attached to various polymer supports. Commercially available examples include the triphenylphosphine on styrene-divinylbenzene copolymers sold by Strem Chemicals and Aldrich Chemical Co., and the triorganophosphine functionalized polysiloxanes (Deloxan®, sold by Degussa AG, Hanau, Germany). Many other similar suitable supports are known or can be readily prepared by methods known to those skilled in the art.

Large, electron-donating trialkylphosphines such as triisopropyl or tricyclohexylphosphine are preferred because they tend to give more catalytically active ruthenium complexes.

Ruthenium complexes of formula I can be prepared by contacting the ruthenium compound having the formula R22RuA2 as described above, the desired organophosphorus ligand PR3, wherein the molar ratio of PR3 to the ruthenium compound is at least 2:1, and an organic solvent with gaseous hydrogen. The solution is stirred, heated, and then the ruthenium complex is optionally isolated from the organic solvent.

Solvents useful in the preparation of ruthenium complexes according to the present invention must be inert to hydrogenation under the reaction conditions, must be liquid under the reaction conditions used, and must be capable of dissolving sufficient ruthenium starting material and hydrogen to produce the desired ruthenium complex.

Although the solvent used is usually and preferably anhydrous, this is not a strict requirement. While the amount of water present is usually and preferably less than about 0.01 moles of water per mole of nitrile, larger amounts of water, up to about 0.1 to about 1 mole of water per mole of nitrile, generally do not produce significant amounts of alcohol byproducts. In the case of a hydrophobic nitrile and hydrophobic solvent, large amounts of water, even a second liquid phase, can be present and not interfere with normal hydrogenation. Suitable solvents include non-condensed C6-C12 benzene hydrocarbons and C1-C18 alkyl derivatives thereof, linear or branched saturated aliphatic or alicyclic C5-C30 hydrocarbons, C2-C12 aliphatic ethers, saturated aliphatic cyclic C4-C12 mono- or diethers or C7-C14 aromatic ethers, or mixtures thereof. The term "non-condensed benzene hydrocarbons" means that when more than one benzene ring is present in the hydrocarbon, the rings are isolated and not condensed together. Thus, the term includes biphenyl but not naphthalene.

Suitable solvents further include the amines, especially those amines prepared by hydrogenation of the above nitriles, which are liquid at the reaction temperature. Typical examples of specific solvents that can be used are ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, amylamine, azacycloheptane, 2-methylpentamethylenediamine and hexamethylenediamine, xylene, hexamethylbenzene, biphenyl, n-octadecylbenzene, benzene, toluene, pentane, cyclopentane, cyclohexane, methylcyclohexane, hexane, isooctane, decane, cyclodecane, tetrahydrofuran, p-dioxane, 2,5-dimethyltetrahydrofuran, methyltetrahydrofurfuryl ether, dimethyl ether, 1,2-dimethoxyethane, diglyme, diethyl ether, diisopropyl ether, anisole, diphenyl ether and mixtures thereof.

Preferred solvents include ammonia, THF, t-butyl methyl ether, toluene, n-amylamine, n-butylamine, 2-methylpentamethylenediamine and hexamethylenediamine. Most preferably, when the amine product of the hydrogenation is a liquid at reaction temperature, the same amine product is used as the reaction solvent. For example, butylamine can be used as the solvent when butyronitrile is hydrogenated, or hexamethylenediamine can be used as the solvent when adiponitrile is hydrogenated.

The hydrogen feedstock comprises hydrogen gas or a mixture of hydrogen gas with inert gases such as N2, He, Ne or Ar. Pure gaseous hydrogen is preferred. Mixtures comprising carbon monoxide, such as "synthesis gas", are unacceptable because CO reacts with the desired ruthenium complex to produce a carbonyl complex.

The partial pressure of hydrogen should be between about 100 kPa and about 15,000 kPa. The preferred pressure is from about 700 kPa to about 7,000 kPa. Higher pressures may be used, but are not necessary and generally do not justify the expense of the more specialized equipment required.

Because of the two-phase medium, effective stirring is required to provide sufficient contact of the gaseous hydrogen with the liquid phase so that the hydrogenation reaction can proceed.

The temperature employed may be from about -30°C to about 200°C. The preferred range is from about 20°C to about 100°C. If desired, the ruthenium complex may be isolated by one of a variety of methods, such as evaporation of the solvent, crystallization by cooling, or precipitation by addition of a second organic solvent which is a poor solvent for the ruthenium complex. The exact isolation method will depend on the amount and nature of the organic solvent used in the preparation. It is desirable to maintain a hydrogen atmosphere as much as possible during handling and isolation of the ruthenium complex to avoid loss of hydrogen from the ruthenium complex.

The process of the present invention is applicable to the preparation of ruthenium complexes with a very wide range of ligands. It provides for the preparation of three classes of ruthenium complexes as given below with their general formula

Class I: RuH2 (PR3 )4

Class II: RuH2L(PR3)3

Class III: RuH2 L2 (PR3 )2

as well as a new class of ruthenium complex, RuH₂L¹₃(PR₃), class IV. L, L¹ and R are as defined above for formula I. Some compounds of classes I and II are fairly well known, but class III complexes are rare.

Dihydrogen ligands present in certain ruthenium complexes of formula I can be replaced by dinitrogen ligands. In complexes where L is H2, either one or all such Ls can be replaced by dinitrogen to produce, for example, RuH2(H2)(N2)(PR3)2 or RuH2(N2)2(PR3)2, hereinafter referred to as "dinitrogen complexes". For example, sparging a solution of RuH2(H2)2(PCy3)2 with nitrogen gas, thereby removing hydrogen from the solution, results in rapid and quantitative conversion to RuH2(N2)2(PCy3)2. This stable bis(dinitrogen) complex, which represents a completely new class of ruthenium complexes, was isolated and clearly characterized by X-ray crystallography. It contains two cis-hydride ligands, two cis- Dinitrogen ligands and two trans-tricyclohexylphosphine ligands arranged octahedrally around ruthenium.

Dinitrogen complexes are often more stable than dihydrogen complexes, for example when the catalyst is placed under a protective nitrogen atmosphere during storage, during preparation of feeds for a reaction, or during product separation or catalyst recycling.

Solvents useful in preparing the dinitrogen complexes of the present invention should not themselves be capable of displacing L-ligands to produce complexes that incorporate the solvent. Suitable solvents for preparing dinitrogen complexes are hydrocarbons including unfused C6-C12 benzene hydrocarbons and C1-C18 alkyl derivatives thereof, as well as linear or branched saturated aliphatic or alicyclic C1-C30 hydrocarbons. Mixtures of hydrocarbons may also be used, such as "petroleum ethers," typically characterized by boiling range. The term unfused benzene hydrocarbons means that when more than one benzene ring is present in the hydrocarbon, the rings are isolated, not fused together. Thus, the term includes biphenyl but not naphthalene. Particularly preferred solvents include toluene, pentane, hexane and petroleum ether with a boiling range of about 35º to about 60ºC.

Agitation is required to ensure sufficient gas-liquid mass transfer, including both the dissolution of dinitrogen gas in the reaction solution and the loss of dihydrogen from the solution, and can be provided by any suitable method, such as stirring or gas diffusion.

The temperature used for this reaction is normally between about -80ºC and about 100ºC. The preferred temperature is about 15ºC to about 30ºC. Higher temperatures increase the reaction rate but adversely affect the stability of the ruthenium complexes.

Pressure is not an important variable; normal atmospheric pressure is preferred, although higher or lower pressures can be used if desired.

The reaction time required is determined primarily by the efficiency with which the gas is contacted and dihydrogen is removed from the reaction mixture. With temperatures below about 30ºC, the reaction time is not critical; reaction times longer than the minimum strictly required time can be used since the dinitrogen complexes are stable at these temperatures. With reaction temperatures above about 30-40ºC, the reaction time should be kept at an empirically determined minimum to avoid unnecessary decomposition of the dinitrogen complexes. The progress of the reaction can be followed spectroscopically by IR or NMR, with phosphorus NMR being particularly useful. Once the minimum strictly required reaction time is thus determined, it will remain constant as long as the reaction conditions are not changed.

Dihydrogen or dinitrogen ligands in the complexes, such as RuH₂(H₂)₂(PR₃)₂, RuH₂(H₂)(N₂)(PR₃)₂, RuH₂(N₂)₂(PR₃)₂, RuH₂(H₂)(PR₃)₃ and RuH₂(N₂)(PR₃)₃, can be replaced by other Electron pair donor ligands can be replaced to give other complexes. Examples of such electron pair donors that are particularly relevant to the present invention include dihydrogen, dinitrogen, and nitriles, which are some of the organic reactants, intermediates, products, and solvents of the hydrogenation reactions of the present invention. Alcohols, amines, imines, and aldehydes are also useful as electron pair donors. For complexes such as RuH2(H2)2(PR3)2 and RuH2(N2)2(PR3)2, either one or both of the dihydrogen or disitrogen ligands can be replaced by added electron pair donors to give other ruthenium complexes with amine, alcohol, imine, ether, nitrile, ester, amide, alkene, alkyne, ketone, or aldehyde ligands. In some cases, mixtures of the ruthenium complexes can be obtained by introducing two or more different electron pair donor ligands: it is not necessary to purify such mixtures; they can be used directly in hydrogenation reactions. For example, the complexes produced when the added electron pair donor ligands are nitriles, referred to hereinafter as "nitrile complexes", do not need to be purified before use in hydrogenations. NMR and IR spectra of nitrile complexes typically indicate the presence of hydride, phosphine, dinitrogen and nitrile ligands. Nitrile complexes can be preformed or they can form in situ upon mixing of the catalyst with nitriles in a hydrogenation reaction.

Solvents useful in preparing the complex include those described above for preparing dinitrogen complexes, as well as the added ligand itself, provided that it is a liquid at the reaction temperature and is capable of sufficiently dissolving the reactants to allow the reaction to take place.

The temperature, pressure and agitation requirements are as described above for the preparation of dinitrogen complexes. The preferred temperature and pressure are ambient, i.e., about 15°C to about 25°C and 1 atmosphere. It is not necessary that the reactants be completely dissolved for the reaction to occur. As long as there is some solubility and sufficient agitation, the reaction will proceed. Typically, ligand exchange is rapid, complete within minutes of mixing. The product complexes can be isolated by removal of the solvent and filtration, or can be used without isolation.

If the reaction mixture is allowed to remain in contact beyond the time required for ligand exchange, and especially if temperatures above ambient are used, secondary reactions may occur. For example, in the presence of hydrogen, nitrile complexes may be partially hydrogenated to imine complexes. The necessary hydrogen may be added intentionally or may be that released from a dihydrogen complex by ligand exchange. In another embodiment, when amines are used in ligand exchange to prepare amine complexes, the amine complex may be dehydrogenated to an imine complex. Such imine complexes are useful catalysts in their own right. These secondary hydrogenation and dehydrogenation processes may result in mixtures of various nitrile, imine and amine complexes that can be used in hydrogenation reactions without purification.

The complexes with the electron pair donor ligand described above can, under certain conditions, be more stable than the dihydrogen complexes from which they can be obtained. This increased stability facilitates storage and recycling of the catalyst.

The ruthenium complexes of the present invention have utility as catalysts. They are useful in catalytic hydrogenation reactions, for example, in the reduction of olefins, in the reduction of nitro compounds to amines, and especially in the reduction of nitriles, which are generally difficult to hydrogenate catalytically, to amines. The most important commercial application of these catalysts is believed to be in the reduction of adiponitrile to either 6-aminohexane nitrile or to hexamethylenediamine, or to mixtures of the two.

There are no reported examples of Class IV compounds with simple monodentate L. Complexes with the apparent stoichiometry RuH₂L¹₃(PR₃) can be formed in organic solvents. The molar ratio of PR₃ to ruthenium compound can range from 1 to <2 moles of PR₃ to 1 mole of ruthenium compound. Preferably, only one equivalent of PR₃ is provided per equivalent of ruthenium compound. These Class IV complexes exhibit even greater hydrogenation activity than Class I-III ruthenium complexes. In aromatic solvents, the arene complexes, (arene)RuH₂(PR₃), can form, but such arene complexes have less activity for hydrogenation reactions than the complexes of the present invention prepared in nonaromatic solvents and are not preferred. No examples of RuH2(PR3)L3 with simple monodentate L have been reported, probably because such complexes are very labile and difficult to isolate, purify and characterize. An advantage of the present invention is that isolation and purification are not necessary. The ruthenium complexes of class IV or Formula II can be prepared and used as catalysts in situ.

There are no generally applicable processes for preparing monomeric ruthenium complexes, such as RuX2(PR3)3, RuHX(PR3)3 and RuX2(PR3)4. The particular ruthenium complex or complexes of formula I or II produced by the process of the present invention will depend on the choice of PR3, L or L1 and the reaction conditions, such as the PR3/Ru ratio used. In some cases a single ruthenium complex may dominate. In other cases a mixture of ruthenium complexes with varying L may be obtained. In general it is not necessary to prepare a single ruthenium complex pure, since mixtures of complexes are also very useful for hydrogenation reactions. The primary advantage of the present invention is that such catalysts do not have to be isolated, but can be generated for hydrogenation reactions and used in situ.

The particular class of ruthenium complex produced by the present invention depends to a large extent on the steric bulk of the phosphorus ligand(s) used. The concept of cone angle, described by CA Tolman in Chemical Reviews, 1977, Vol. 77, pp. 313-348, is a valuable tool for classifying PR3 ligands and understanding how their steric bulk determines which class of complex is obtained. Small ligands with cone angles of about 130° or less, such as the tri-n-alkylphosphines, including, for example, tributylphosphine, favor the formation of Class I complexes. Medium-sized ligands with Cone angles of 140-150º favor the formation of class II complexes. Large ligands with cone angles of 160-180º favor the formation of class III complexes.

Since each R substituent group on PR3 can be varied independently, the steric volume of PR3 can be continuously varied over a wide range. Since the steric size can be continuously varied, the boundaries between the classes of ruthenium complexes are not sharply drawn. As a result, in the process of the present invention, for cases where Class II complexes can be prepared, mixtures are often obtained which additionally contain some Class I or Class III complexes. In such cases, the exact composition of the mixture obtained can be controlled to a certain extent by adjusting the molar ratio of organophosphorus ligand to ruthenium compound used during preparation. For example, when obtaining mixtures of Class I and Class II complexes, the formation of Class I complexes can be favored by using a large excess of organophosphorus ligand in the preparation, while the formation of Class II complexes can be favored by using only three PR₃ per ruthenium compound, i.e., little or no excess of ligand. Similar considerations are applied to the control of mixtures of Class II, III, and IV complexes. Class III complexes can be favored by using only two PR₃ per ruthenium, while those of Class II can be favored by using three or more PR₃ per ruthenium. Class II, III, and IV complexes are preferred for hydrogenation reactions. Class III and IV complexes are especially preferred, and especially those with large phosphorus ligands which substantially prevent the formation of Class II complexes, even in the presence of excess organophosphorus ligand. Class III complexes in which PR3 is PCy3 are most preferred because they are generally more stable than Class IV complexes.

Each class of ruthenium complex, i.e., RuH2(PR3)4, RuH2(H2)(PR3)3, or RuH2(H2)2(PR3)2, has a characteristic NMR pattern based on the symmetry of the complex. For example, cis- RuH2(PR3)4 with octahedral geometry around Ru contains two different types of PR3 ligands: two equivalent PR3, each of which is trans to an H ligand, and two equivalent PR3 ligands trans to each other. This results in a phosphorus NMR spectrum described as an A2X2 pattern, which, as will be understood by those skilled in the art, results in a pair of triplets of equal intensity. A complex but characteristic multiplet is observed for the hydride signal in the proton NMR and integration should be correct for four PR3 ligands and two hydride H.

RuH2(H2)(PR3)3 typically shows only single lines in both proton and phosphorus NMR, due to rapid exchange of ligands and H2 hydride, but integration of proton NMR should be correct for four hydrides and 3 PR3 ligands. A valuable diagnostic for identifying RuH2(H2)(PR3)3 species is their tendency to rapidly exchange H2 for N2 under a dinitrogen atmosphere, producing RuH2(N2)(PR3)3, which has a more distinctive NMR signature. Phosphorus NMR shows an A2X pattern, i.e. a triplet of intensity one and a doublet of intensity two. The proton NMR spectrum includes a characteristic pair of complex multiplets of equal intensity, indicating two nonequivalent hydrides, as expected for an octahedral geometry with a hydride trans to a PR₃ ligand and the other trans to an N2 ligand would be expected. RuH2(H2)(PR3)3 can be easily recognized by comparing the proton and phosphorus NMR spectra of a solution prepared under H2 with a solution prepared under N2.

Finally, RuH2(H2)2(PR3)2 exhibits a single-line phosphorus NMR spectrum. Under high resolution conditions, the hydride signal in the proton NMR spectrum appears as a triplet due to coupling to two equivalent PR3 ligands, and the relative intensities of the hydride and ligand protons integrate correctly for a ratio of six hydrides and 2 PR3 ligands. RuH2(H2)2(PR3)2 can also be distinguished by its tendency to exchange H2 for N2 to produce RuH2(N2)2(PR3)2. These dinitrogen complexes show a single line in their proton-decoupled phosphorus NMR which becomes a triplet with proton coupling, confirming the presence of two hydrides. The hydride signal in proton NMR appears as a triplet coupled to two equivalent PR3 phosphorus nuclei. The generation of RuH2(H2)2(PR3)2 can be provided by its reaction with nitrogen to form RuH2(N2)2(PR3)2, which can be determined by comparing proton and phosphorus NMR spectra of a solution prepared under H2 with a solution prepared under N2.

The ruthenium complexes of formula I have utility as catalysts. They are useful in catalytic hydrogenation reactions, for example in the reduction of alkenes to alkanes, in the reduction of nitro compounds to amines, and especially in the reduction of nitriles, which are generally difficult to hydrogenate catalytically, to amines. The most important commercial use of these catalysts is believed to be the reduction of adiponitrile to either 6-aminohexanenitrile or to hexamethylenediamine or to mixtures of these two compounds.

Suitable nitrile substrates useful in these hydrogenation processes of the present invention include those having at least one CN group capable of being hydrogenated to the corresponding primary amine. Typically, the nitrile substrate is a monomeric material having one or two CN groups. However, the nitrile substrate may also be oligomeric or polymeric, having either regularly occurring or occasional CN functional groups, including, for example, fluoronitriles such as F(CF2CF2)nCH2CH2CN, where n ranges from 2 to about 6. Complete reduction of a dinitrile to a diamine is one embodiment of the present hydrogenation processes.

Suitable nitrile substrates include the classes of linear or branched saturated aliphatic C2-C18 mono- and C3-C19 dinitriles and phenyl derivatives thereof, saturated alicyclic C4-C13 mono- and C5-C14 dinitriles, linear or branched olefinically unsaturated aliphatic C3-C18 nitriles, olefinically unsaturated alicyclic C6-C13 nitriles, aromatic C7-C14 mono- and dinitriles, heterocyclic nitrogen and Oxygen C6-C8 mononitriles, C3-C4 cyanoalkanoamides, saturated aliphatic C2-C12 cyanohydrins or hydroxynitriles or mixtures of the nitriles described above, where the nitriles may also contain non-impairing substituents.

Examples of some substituents that generally do not interfere with the desired hydrogenation reaction include hydroxyl, amine, ether, alkyl, alkoxy and aryloxy. For example, cyanohydrins and hydroxynitriles are both acceptable nitriles. Unsaturated hydrogenatable substituents such as esters, amides, aldehydes, imine, nitro, alkene and alkyne are permissible insofar as they interfere with the hydrogenation of the Nitrile groups, but they can themselves be partially or completely hydrogenated during the course of nitrile hydrogenation. For example, 2-pentenenitrile can be completely hydrogenated to aminopentane. Carboxylic acids are generally not acceptable substituents because they react with the catalyst and deactivate it.

Typical examples of specific nitriles applicable in the process of the invention include: acetonitrile (C2), propionitrile (C3), butyronitrile (C4), valeronitrile (C5), capronitrile (C6), 2,2- dimethylpropanenitrile, oenanthonitrile (C7), caprylonitrile (C5), pelargononitrile (C9), caprinitrile (C10), undecanonitrile (C11), lauronitrile (C12), tridecanonitrile (C13), myristonitrile (C14), pentadecanonitrile (C15), palmitonitrile (C16), Margaronitrile (C17), stearonitrile (C18), phenylacetonitrile (benzylnitrile), naphthylacetonitrile, malononitrile, succinonitrile, glutaronitrile, 2-methylglutaronitrile, adiponitrile, acrylonitrile, methacrylonitrile, 2-methyleneglutaronitrile, 1,4-dicyano-2-butene 1 ,4-dicyano-1-butene, dodecanedinitrile, 3-butenenitrile, 4-pentenenitrile, 3-pentenenitrile, 2-pentenenitrile, 2-hexenenitrile, 2-heptenitrile, glycolonitrile (formaldehyde cyanohydrin), hydroacrylonitrile (ethylene cyanohydrin), epicyanhydrin (gamma-cyanopropylene oxide), lactonitrile, Pyruvonitrile, cyclohexanecarbonitrile, benzonitrile, o-tolylnitrile, m-tolylnitrile, p-tolylnitrile, anthranilic acid nitrile, m-aminobenzonitrile, p-aminobenzonitrile, 1-naphthonitrile, 2-naphthonitrile, phthalonitrile, isophthalonitrile, terephthalonitrile, mandelic acid nitrile, 2-pyridine nitrile, 3-Pyridinenitrile, 4-Pyridinenitrile or 2-Furylacetonitrile.

Preferred nitriles in the process are adiponitrile, 2-methylglutaronitrile and dodecanedinitrile.

The present hydrogenation processes can be carried out in the neat state, i.e., no solvent, provided that the nitrile and product amine are liquids at the reaction temperature employed and that the catalyst is sufficiently soluble therein. However, the use of a solvent is preferred to facilitate contacting of the reactants and removal of heat. The solubility of the respective materials in the solvent (or mixture of solvents) should be significantly large enough to initiate and sustain the hydrogenation process.

Solvents that can be used in these hydrogenation processes must be inert to hydrogenation under the reaction conditions and have sufficient solubility for the substrate nitrile and the catalyst.

Although the solvent used is usually and preferably anhydrous, this is not a strict requirement. While the amount of water present is usually and preferably less than about 0.01 mole of water per mole of nitrile, larger amounts of water, up to about 0.1 to about 1 mole of water per mole of nitrile, generally do not produce significant amounts of alcohol byproducts. In the case of a hydrophobic nitrile and hydrophobic solvent, large amounts of water, even a second liquid phase, can be present and they do not interfere with normal hydrogenation. Suitable solvents include non-condensed C6-C12 benzene hydrocarbons and C1-C18 alkyl derivatives thereof, linear or branched saturated aliphatic or alicyclic C5-C30 hydrocarbons, C2-C12 aliphatic ethers, saturated aliphatic cyclic C4-C12 mono- or diethers or C7-C14 aromatic ethers, or mixtures thereof. The term "non-condensed benzene hydrocarbons" means that when more than one benzene ring is present in the hydrocarbon is present, the rings are isolated and not condensed together. Thus, the term includes biphenyl, but not naphthalene.

Suitable solvents further include amines, in particular those amines produced during the hydrogenation of the above nitriles, which are liquid at the reaction temperature. Typical examples of specific solvents that can be used include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, amylamine, azacycloheptane, 2-methylpentamethylenediamine and hexamethylenediamine, xylene, hexamethylbenzene, biphenyl, n-octadecylbenzene, benzene, toluene, pentane, cyclopentane, cyclohexane, methylcyclohexane, hexane, isooctane, decane, cyclodecane, tetrahydrofuran, p- dioxane, 2,5-dimethyltetrahydrofuran, methyltetrahydrofurfuryl ether, dimethyl ether, 1,2-dimethoxyethane, diglyme, diethyl ether, diisopropyl ether, anisole, diphenyl ether and mixtures thereof.

Preferred solvents include ammonia, THF, t-butyl methyl ether, toluene, n-amylamine, n-butylamine, 2-methylpentamethylenediamine, and hexamethylenediamine. Most preferably, when the amine product of the hydrogenation is a liquid at the reaction temperature, the same amine product is used as the reaction solvent. For example, butylamine can be used as the solvent when butyronitrile is hydrogenated, or hexamethylenediamine can be used as the solvent when adiponitrile is hydrogenated.

The amount of catalyst used can vary from about 10 mole percent based on nitrile to be hydrogenated to about 0.01 mole percent. The preferred amount of catalyst is between about 1% and about 0.1% on a molar basis of the amount of nitrile to be hydrogenated. Larger or smaller amounts of catalyst can be used at the expense of catalyst cost or reaction time, respectively.

Excess organophosphorus ligand may be present if desired and will not interfere with the hydrogenation. Although excess organophosphorus ligand is not required, the presence of excess organophosphorus ligand ensures that sufficient organophosphorus ligand is always present to stabilize the ruthenium catalyst, even if adventitious oxygen oxidizes a small amount of organophosphorus ligand to the corresponding oxidation product of the ligand, e.g., a phosphine oxide, or other side reactions decompose portions of the organophosphorus ligand. Oxidation products of the ligand generated in this manner may also be present and will not interfere with the hydrogenation reactions. The molar ratio of excess organophosphorus ligand to ruthenium may vary from zero to about 60 or even more. The preferred molar ratio is between zero and about 30, with a molar ratio of about 2 to about 25 being most preferred.

The hydrogenation can be carried out at any convenient temperature from about 0°C to about 200°C. Lower temperatures require prolonged reaction times, while higher temperatures reduce catalyst life and reduce the yield of primary amine as the desired product. The preferred temperature is in the range of about 60° to about 120°C, with about 80° to about 100°C being most preferred.

The starting material for hydrogen can be hydrogen gas or mixtures of hydrogen gas with other gases that do not interfere with the desired hydrogenation. Non-interfering Examples of gases include inert gases such as helium, argon and nitrogen. Oxygen and carbon monoxide should be avoided as they can react with the catalysts.

The pressure used can be from about 100 kPa (1 atmosphere) to about 15,000 kPa or even higher. Elevated pressures are preferred because the solubility of hydrogen is increased, resulting in higher reaction rates. However, pressures above about 7,000 kPa to about 10,000 kPa are generally avoided because of the high cost of equipment capable of operating at such pressures. The preferred pressure is in the range of about 3,550 kPa to about 10,000 kPa. Pressures between about 5,000 kPa and about 7,000 kPa are most preferred.

The hydrogenation of nitriles is a two-phase reaction. Therefore, it is important to provide sufficient gas-liquid contact to allow the gaseous hydrogen to dissolve in the liquid reaction phase. Sufficient gas-liquid contact can be facilitated by any of several agitation methods known to those skilled in the art. Typical methods include dispersing gas below the liquid surface in a tank reactor, agitating the liquid in a tank reactor to draw the gas into the liquid and create bubbles, using packing in a tower reactor to obtain a high liquid surface area, or using a bubble column reactor where bubbles of gas are introduced into the reactor and rise through the liquid phase.

The catalyst comprising at least one ruthenium complex of formula I is also useful in a selective hydrogenation process in which a dinitrile is partially hydrogenated to give an aminonitrile comprising contacting the dinitrile with gaseous hydrogen in the presence of the catalyst comprising at least one complex of formula II, RuH2L'3(PR3), where L' is a neutral electron pair donor ligand selected from: H2, N2, nitriles, amines, alcohols, ethers, esters, amines, alkenes, alkynes, aldehydes, ketones, imines, and then stirring the dinitrile, hydrogen and catalyst for a period of time selected to favor the yield of the aminonitrile over the yield of a diamine. For example, the main intermediate in the hydrogenation of adiponitrile, 6-aminocapronitrile, can be produced in high yield if the hydrogenation is stopped at an intermediate stage. This aminonitrile can then be directly hydrolyzed and polymerized to nylon 6. The present invention also provides an in situ process for the selective hydrogenation process in which the dinitrile is added to the ruthenium complex catalyst preparation comprising the ruthenium compound R22RuA2, the organophosphorus ligand PR3, at least one L' ligand, gaseous hydrogen and the organic solvent, thus allowing catalyst formation and selective hydrogenation all in one step.

The dinitrile used in these selective hydrogenation processes can be any aliphatic dinitrile comprising from about 3 to about 14 carbon atoms, but preferably comprising about 6 to about 12 carbon atoms. Preferably, the carbon atoms are arranged in a linear or branched chain. Particularly preferred examples of dinitriles and their product include adiponitrile hydrogenated to 6-aminocapronitrile, 2-methylglutaronitrile hydrogenated to a mixture of two isomeric aminonitriles (5-amino-2-methylvaleronotrile and 5-amino-4-methylvaleronitrile) and dodecanedinitrile hydrogenated to 12-aminododecanonitrile.

The amount of organophosphorus ligand excess to the catalyst, solvent, temperature, pressure, agitation requirements, and hydrogen starting materials are the same as discussed above for the hydrogenation of nitriles to primary amines.

The desired product of the selective reduction, an aminonitrile, is an intermediate in one embodiment of the present hydrogenation process which ultimately leads to the production of a diamine. The concentration of aminonitrile in the reaction mixture passes through a maximum as the reaction proceeds. An object of this embodiment of the present invention is to maximize the concentration of aminonitrile in the reaction mixture with the highest possible conversion of the starting dinitrile. The yield of aminonitrile and the location of the maximum with respect to the dinitrile conversion depend on the operating conditions such as temperature, hydrogen pressure, amount and type of catalyst, dilution of the starting dinitrile as well as the type of solvent. These variables in turn affect the optimal contact time for the reaction. Conventional nitrile hydrogenation catalysts often give selectivities to aminocapronitrile (ACN) that approach those statistically expected assuming that the two ends of the dinitrile are hydrogenated independently and at comparable rates. In contrast, the catalysts of the present invention give aminonitrile selectivities that are higher than those statistically expected.

The optimum reaction time of the present invention required to favor the production of an amino nitrile needs to be determined only once for a given set of reaction conditions. Once the optimum has been determined, it will remain constant as long as the reaction conditions, such as catalyst, reactant concentrations, temperature and pressure, are kept constant.

The abbreviations used throughout are:

ACN Aminocapronitril

ADN Adiponitrile

CPI 2-cyanocyclopentylimine

DMF N,N-dimethylformamide

Dytek A® 2-Methylpentamethylenediamine

Et Ethyl

HMD Hexamethylenediamine

HMI Hexamethyleneimine (Akaazacycloheptane)

Me Methyl

MGN 2-methylglutaronitrile

MTBE Methyl t-butyl ether

Bui Isobutyl

Butyl n-butyl

COD Cyclooctadien

COT Cyclooctatrien

d doublet

L is any neutral 2-electron donor ligand (including H2, N2, phosphines, etc.)

m Medium intensity IR band or NMR line multiplet

N112 Aminocapronitril

P triorganophosphine (e.g. triphenylphosphine)

Ph Phenyl

Pri Isopropyl

q Quartet

s IR band of high intensity or NMR line singlet

t triplet

THA Tetrahydroazapin

THF Tetrahydrofuran

w IR band of weak intensity

DEFINITIONS

Yield: moles of product produced / moles of reactant used · 100%

Selectivity: moles of product produced / moles of reactant consumed · 100%

EXAMPLE 1 Preparation of RuH₂(H₂)₂(PCy₃)₂ and RuH₂(N₂)₂(PCy₃)₂

A solution of 0.0584 g (0.18 mmol) of (COD)Ru(2-methylallyl)z and 0.1159 g (0.41 mmol) of tricyclohexylphosphine in 5 mL of tetrahydrofuran was heated to 70°C under 860 kPa H2. After 1.3 h, the reaction was cooled and placed in a glove box with N2 atmosphere. 31P NMR of a sample prepared under nitrogen showed the product to be a mixture containing predominantly RuH2(H2)2(PCy3)2 and the related dinitrogen complexes generated therefrom via reaction with the nitrogen atmosphere (e.g., RuH2(N2)2(PCy3)2). Evaporation of a solution using a stream of nitrogen completely converted the dihydrogen complex to RuH2(N2)2(PCy3)2 as shown by 31P and 1H NMR.

COMPARISON EXAMPLE 2 A. Preparation of (h⁶-toluene)RuH₂(PCy₃) in toluene solvent

A solution of 0.034 g (0.1 mmol) of (COD)Ru(2-methylallyl)2 and 0.056 g of PCy3 (0.2 mmol, 2P/Ru) in 5 mL of toluene was heated to 70 °C in a Fisher-Porter tube under 860 kPa of H2. After 2 h, the reaction was cooled and transferred to the glove box. The product was isolated by removing the solvent in vacuo. 31 P and 1H NMR identified the product as (h6-toluene)RuH2(PCy3). No RuH2(H2)2(PCy3)2 or RuH2(N2)2(PCy3)2 was detected. ³¹P {¹H}: 78.96 ppm (s), becomes a triplet if ¹H coupling is allowed, JPH = 42.6 Hz, proving that two hydride ligands are present. ¹H: 10.6 ppm (d, 2H, hydrides, JPH = 42.6 Hz, proving the presence of a single phosphine ligand), 5-5.25 (m, 5H, aromatic protons on coordinated toluene).

B. ADN hydrogenation with (h⁶-toluene)RuH₂(PCy₃)

A solution containing 0.08 mmol (h⁶-toluene)RuH₂(PCy₃) and 27.7 mmol ADN in 35 mL of toluene was heated to 60°C in a stirred autoclave under 7000 kPa H₂. After 23 hours, the conversion of ADN reached 32%.

For comparison, a mixture of 0.0704 g of RuH2(H2)2(PCy3)2 (0.1 mmol) prepared as below and 2.9154 g of ADN (27 mmol, 270 ADN/Ru) in 35 mL of toluene was heated to 60°C in a stirred autoclave under 7000 kPa H2. After 20.75 h, the composition consisted of 15% ADN, 70% ACN and 15% HMD. Thus, the conversion of ADN had reached 85%, with a selectivity to ACN of 82%.

Preparation of RuH2(H2)2(PCy3)2 from (COD)RuCl2

A mixture of 1.74 g of Ru(COD)Cl2 (6.2 mmol), 3.49 g of PCy3 (12.5 mmol), 2.14 g of NaOH (54 mmol), 0.0579 g of benzyltriethylammonium chloride (0.25 mmol of phase transfer catalyst), 15 mL of toluene and 5 mL of water was stirred for 7.5 hours under 7000 kPa of hydrogen at 40 °C. After cooling under hydrogen, the reaction mixture was worked up in a nitrogen-filled glove box. The solid product was isolated by filtration, washed with 10 mL of heptane and dried under a nitrogen stream to give 4.0 g of pale yellow powder (96% yield). The product was identified by comparing its 'H and 31P NMR values with literature values.

EXAMPLE 3 Preparation of PnBu₃ complexes in toluene solvent

A solution of 0.379 g (0.12 mmol) of (COD)Ru(2-methylallyl)2 and 0.0482 g (0.24 mmol) of PnBu3 in 5 g of toluene was heated to 70 °C in a Fisher-Porter tube under 860 kPa of H2. After 1.7 h, the reaction was cooled and placed in the glove box. The solvent was removed in vacuo. 31P and 1H NMR showed the product to be a mixture of about 50% RuH2(H2)(PnBu3)3, 1H: - 8.1 (br, s, hydrides); 3¹P{¹H}: 33.5 (s), 25% RuH₂(N₂)(PnBu₃)3, 1H: -9.3 (dtd), -13.8 (m) both are hydrides; 3¹P{¹H}: 28.8 (d, 2P), 17.1 (t, 1P), JPP 19.5 Hz), and 25% (h⁶-toluene)RuH₂(PnBu₃) was, 1H: -10.27 (d, hydrides, JPH 45 Hz), 4.95-5.2 (m, h⁶-toluene aromatic protons). 3¹P{¹H}: 46.3 (s).

EXAMPLE 4 In-situ catalyst preparation using PiPr3 and ADN hydrogenation in n-butylamine solvent

Examples 4A-4D, summarized in the table below, demonstrate that phosphine is required to produce an active and stable catalyst, but that excess phosphine reduces the rate. They also demonstrate in situ catalyst generation and hydrogenation in n-butylamine solvent. SUMMARY OF THE EFFECT OF P/Ru ON ADHYDROGENATION RATE

A. No added phosphine

A solution of 0.03048 g of (COD)Ru(2-methylallyl)2 (0.095 mmol) and 0.9905 g of ADN (9.163 mmol, 96 ADN/Ru) in 40 mL of n-butylamine was heated to 80°C in a stirred autoclave under 7000 kPa H2. After 5 hours, the ADN conversion was less than 5%.

B. PiPr3/Ru = 1

A solution of 0.027 g of (COD)Ru(2-methylallyl)2 (0.084 mmol), 16 μl of PiPr3 (0.081 mmol, 0.96 P/Ru) and 1.08 g of ADN (9.95 mmol, 119 ADN/Ru) in 35 mL of n-butylamine was heated to 80 °C under 7000 kPa 112 in a stirred autoclave. After 4.2 hours the ADN was completely hydrogenated and the yield of HMD was 92%.

C. PiPr3/Ru = 2.4

A solution of 0.0248 g of (COD)Ru(2-methylallyl)2 (0.077 mmol), 36 μl of PiPr3 (0.184 mmol, 2.4 P/Ru) and 1.21 g of ADN (11.2 mmol, 145 ADN/Ru) in 40 mL of n-butylamine was heated to 80 °C in a stirred autoclave under 7000 kPa H2. After 7 hours, the ADN was completely hydrogenated and the yield of HMD was 93%.

D. PiPr3/Ru = 6

A solution of 0.0256 g of (COD)Ru(2-methylallyl)2 (0.08 mmol), 94 μl of PiPr3 (0.48 mmol, 6 P/Ru) and 0.99 g of ADN (9.2 mmol, 115 ADN/Ru) in 40 mL of n-butylamine was heated to 80°C in a stirred autoclave under 7000 kPa H2. After 7.3 hours, 99% of the ADN was hydrogenated, yielding 46% ACN and 45% HMD.

EXAMPLE 5 In-situ catalyst preparation using PPh3 and ADN hydrogenation in n-butylamine solvent

A solution of 0.026 g of (COD)Ru(2-methylallyl)2 (0.08 mmol), 0.022 g of PPh3 (0.08 mmol, 1 P/Ru) and 0.87 g of ADN (8 mmol, 100 ADN/Ru) in 35 mL of n-butylamine was heated to 80°C in a stirred autoclave under 7000 kPa H2. After 8.5 hours, 96% of the ADN was hydrogenated, yielding 55% ACN and 31% HMD. The conversion of the intermediate ACN was incomplete.

EXAMPLE 6 Heterogenized Ru catalyst on silica-supported phosphine A. Catalyst production

A silica supported phosphine was prepared by grafting diphenylphosphinopropylsilyl groups onto a commercially available silica support. The resulting material contained 0.4 wt% P. The silica support, a Grace-Davison 62 silica support, was dried overnight at 400°C in a dry nitrogen stream. The phosphine was bonded to the surface by refluxing a 25% solution of 2-(diphenylphosphino)ethyltriethoxysilane in dry toluene overnight in the presence of the silica support. The modified support was washed with an excess of dry toluene and the product dried under vacuum. A mixture of (COD)Ru(2-methylallyl)2 (0.028 g, 0.1 mmol) and the silica-supported phosphine (1.55 g, containing 0.2 mmol P) in 10 mL of THF were heated at 70 °C in a Fisher-Porter tube under 860 kPa H2 for 3 h. Removal of the solvent in vacuo gave a brown powder.

B. Hydrogenation of 1,5-cyclooctadiene

An amount of the above catalyst containing an estimated 0.1 mmol of Ru was combined with 10 mmol of 1,5-cyclooctadiene in 15 g of THF. The mixture was stirred in a Fisher-Porter tube under 860 kPa of H2 for 1.5 hours at 20°C. Gas chromatographic analysis after 1.7 hours showed the presence of 28% COD, 46% cyclooctene and 26% cyclooctane. After 5.7 hours the mixture was completely hydrogenated to cyclooctane.

The catalyst was removed by filtration and washed with several small portions of ether and THF. The recycled catalyst was found to still be active for the hydrogenation of 1,5-cyclooctadiene at 70°C and 860 kPa H2.

Claims (4)

1. A process for preparing a ruthenium complex having the formula RuH₂(PR₃)₂L₂, wherein: each PR₃ is an organophosphorus ligand, present as a separate ligand or linked to at least one other organophosphorus ligand PR₃; each R is a substituent independently selected from: H, R', OR', OSiR'₃, NH₂, NHR' and NR'₂, each R' is independently selected from: a hydrocarbyl group and an array of at least two hydrocarbyl groups linked by ether or amine linkages; and each L is a ligand independently selected from: H2 and an additional equivalent of the organophosphorus ligand PR3;; comprehensive the steps: (a) contacting a ruthenium compound having the formula R22RuA2, wherein R2 is a mono- or poly-, cyclic or acyclic alkene ligand present as either two separate ligands or as a single polyalkene ligand, and A is an allyl ligand or a hydrocarbyl-substituted allyl ligand; an organic solvent; and PR3, wherein the molar ratio of PR3 to the ruthenium compound is at least 2:1, with gaseous hydrogen; (b) stirring the solution at a temperature of about -30ºC to about 200ºC; and If necessary, isolating the ruthenium complex from the organic solvent. 2. The process of claim 1, wherein the ruthenium compound is selected from the group consisting of: (allyl)₂RuR22, (1-methylallyl)₂RuR22, (2-methylallyl)₂RuR22, (norbornadiene)RuA₂, (cyclohexadiene)RuA₂, (cycloheptatriene)RuA₂ and (1,5-cyclooctadiene)RuA₂. 3. The process of claim 2, wherein the ruthenium compound is (2-methylallyl)₂Ru(1,5-cyclooctadiene). 4. The process of claim 1, wherein all R substituents are the same and are selected from: a cyclohexyl group, an isopropyl group and an n-butyl group.